1. Field of the Invention
The present invention relates generally to bulk material processing and in particular to a bulk material dryer.
2. Description of the Related Art
Various types of bulk materials are processed in continuous, as opposed to batch, operations. A common such continuous operation involves the removal of moisture from the material being processed. For example, numerous materials, including food and feed, have relatively high moisture contents during certain stages of processing. Such moisture may be present in the raw materials, or it may be added during processing. For example, extruders can be used to cook and form materials with relatively high moisture contents, and dryers are sometimes used in sequence with extruders to remove excess moisture from the extruded products.
A previous type of bulk material dryer includes a cabinet with one or more conveyor passes or runs extending therethrough and ductwork for supplying and receiving heated air located alongside the cabinet. Heated air can be introduced by means of a blower to a lower portion of the cabinet interior for passing upwardly through the material-laden conveyor belts. The heated air can then be collected at the cabinet top and returned to the cabinet side with the air handling equipment. Although heated air can be recirculated with such an arrangement for energy efficiency, certain disadvantages can be encountered. Static air pressure and airflow velocity tend to decrease with distance from the air supply inlets along one side of the cabinet, resulting in uneven airflow and drying. The heated air can bypass much of the material within the dryer cabinet and instead take the shortest route to return air outlets located in the side of the dryer cabinet with the air handling equipment. Uneven product drying and inefficient energy usage can result.
Another problem with some previous dryers is that they occasionally caught fire when particles (e.g. dust and fines) were ignited by the heaters. Various bulk materials, including grain-based food and feed products, can produce flammable dust and fines. The burners and other heat sources of some previous dryers have ignited such combustible particles, and internal dryer fires can cause extensive damage.
Locating the air handling system alongside the dryer in previous dryer designs also tended to increase the floor area requirements thereof, which can be a serious disadvantage in processing facilities with limited floor area.
Previous dryers have had other configurations and air handling system placements; however, heretofore there has not been available a bulk material dryer with the advantages and features of the present invention. The present invention addresses these deficiencies with previous bulk material dryers.